In the word "seat," the onset is the initial consonant or consonant cluster that precedes the vowel. Here, the onset is the consonant "s." The vowel sound that follows is represented by "ea," which together with the onset forms the syllable "seat."
"Onset" is one word.
There will be an onset of bugs to the dead carcass.
I was onset walking on a lOng road.
The onset of winter brought heavy snowfall to the region.
Blow
Sn
Start, Onset
onset
Yes. The onset of night is one word, nightfall.
clinic
onset
The base word in "unseated" is "seat".